Windows Phone 8 Page Navigation - windows-phone-8

Question

I have a problem that I can't really figure out, and I am really desperate now - I've no idea why it's happening:(
So here is the problem: I am writing a kind of Guess that Tune app. The first page is a menu page, that a user can press "Play" button, and he will navigate to a GenreSelectPage where he selects a genre and navigates to a GamePage. I wanted to handle BackButtonPress on GamePage - when a user hits BackButton, he navigates to MainPage, not GenreSelectPage. Here is the code:
private void PhoneApplicationPage_BackKeyPress(object sender, CancelEventArgs e)
{
base.OnBackKeyPress(e);
this.player.Pause();
var result = MessageBox.Show(AppResources.GamePageAlert, "Warning", MessageBoxButton.OKCancel);
if (result == MessageBoxResult.OK)
{
//NavigationService.RemoveBackEntry();
//App.RootFrame.Navigate(new Uri(#"/MainPage.xaml", UriKind.Relative));
}
else
{
this.player.Play();
e.Cancel = true;
}
}
However, I encoountered a big problem here I can't really solve. When I move back to MainMEnu, than go again to GenreSelectPage and choose the same genre, everything is ok - the app navigates to GamePage where there is list of 4 answers. However, if I choose another genre, the listBox at GamePage is populated with 12 or 15 items. On the other hand, when I comment navigation to MainPage and normally go back, everything works alright.
Here is my GenrePage Code:
public GenresPage()
{
InitializeComponent();
this.DataContext = App.ViewModel.GenreHelper;
}
private async void PhoneApplicationPage_Loaded(object sender, RoutedEventArgs e)
{
this.genresListBox.SelectedIndex = -1;
this.progressBar.Visibility = System.Windows.Visibility.Visible;
this.genresListBox.ItemsSource = await App.ViewModel.GenreHelper.GetGenres();
this.progressBar.Visibility = System.Windows.Visibility.Collapsed;
ClearCollections();
}
private static void ClearCollections()
{
if (App.ViewModel.TracksCollection.Count != 0)
{
App.ViewModel.TracksCollection.Clear();
App.ViewModel.TrackCounter = 0;
}
if (App.ViewModel.AnswerCollection.Count > 0)
{
App.ViewModel.AnswerCollection.Clear();
}
}
private async void NavigateToPlay(object sender, RoutedEventArgs e)
{
if (this.genresListBox.SelectedIndex != -1)
{
this.progressBar.Visibility = System.Windows.Visibility.Visible;
await App.ViewModel.GetSongs();
await App.ViewModel.GetAnswers();
this.progressBar.Visibility = System.Windows.Visibility.Collapsed;
NavigationService.Navigate(new Uri(#"/Views/GamePage.xaml", UriKind.Relative));
}
}
UPDATE
On my GamePage I am only assigning DataContext and duration to MediaElement:
public partial class GamePage : PhoneApplicationPage
{
public GamePage()
{
InitializeComponent();
this.DataContext = App.ViewModel;
}
private void PhoneApplicationPage_Loaded(object sender, RoutedEventArgs e)
{
var trackId = App.ViewModel.TracksCollection[App.ViewModel.TrackCounter].Id;
var sampleUri = App.ViewModel.GetSampleUri(trackId);
player.Source = new Uri(sampleUri.AbsoluteUri);
player.Play();
}
private void GetTrackDuration(object sender, RoutedEventArgs e)
{
var player = (MediaElement)sender;
if (player.CurrentState == System.Windows.Media.MediaElementState.Playing)
{
playerSeekBar.Maximum = player.NaturalDuration.TimeSpan.TotalSeconds;
}
}
private void PhoneApplicationPage_BackKeyPress(object sender, CancelEventArgs e)
{
base.OnBackKeyPress(e);
this.player.Pause();
var result = MessageBox.Show(AppResources.GamePageAlert, "Warning", MessageBoxButton.OKCancel);
if (result == MessageBoxResult.OK)
{
//NavigationService.RemoveBackEntry();
//App.RootFrame.Navigate(new Uri(#"/MainPage.xaml", UriKind.Relative));
}
else
{
this.player.Play();
e.Cancel = true;
}
}
}
If anyone can point out what I am doing wrong, I would be really greatful - I am fighting it all day and I have no idea what's causing it.
Thank You very much in advance!!